The conventional rotary type encoder will be explained with reference to JP-A-11-325972. According to this publication, the rotary type encoder employs a method of correcting an absolute angular error generated due to the core fluctuation between a rotary disk and a rotation shaft to which the rotary disk is fixed thereby to improve the positional detection accuracy of an encoder apparatus. That is, the method includes a core fluctuation amount detection process of detecting an amount of the core fluctuation between the rotary disk and the rotation shaft to which the rotary disk is fixed, an absolute angular error determining process of determining an absolute angular error from the amount of the core fluctuation, a correction value determining process of determining a correction value for correcting the absolute angular error, and a positional data correcting process of adding the correction value to the an absolute angular position data outputted from the encoder apparatus to correct the absolute angular position data.
According to such a rotary type encoder, it is possible to obtain the absolute angular position data with a high accuracy from which error due to the core fluctuation is eliminated.
However, in the conventional technique, when error data divided into many regions is stored in a storage element in order to secure the accuracy of the absolute angular error, the size of the storage element becomes large according to the increase of the storage capacity and so the size of the rotary type encoder becomes large. In particular, according to the increase of an N frequency component of one revolution, the number of the error data increases, and hence there arises a problem that the storage capacity increases and so the size of the storage element becomes large.